The effect of protective pillars on the deformation of mine shafts

Summary Mine shafts have traditionally been protected by leaving the ore in the immediate surroundings of the shafts in place as a pillar. Empirical rules are used to determine the dimensions of these protective pillars. The face element principle introduced by Salamon has been used to compute functions which express the influence of mining in a horizontal seam on the rock mass above it. Values have been calculated for the tilt, distortion, horizontal and vertical strain, curvature, and vertical stress along a shaft for various values of Poisson's ratio, seam depth, pillar radius, mining geometry, and closure over the mined area. The results are compared with those obtained using empirical ideas, particularly the angle of draw concept in determining pillar size. It appears that the depth of the seam is of major significance and that no pillar is needed for the protection of a shaft when the mined seam is beyond a certain depth. On the other hand it is possible, at all depths, to replace the protective action of a shaft pillar by other mining schemes. A significant amount of information which has been published on experience gained during the mining of shaft pillars tends to indicate that in many mines shaft pillars are excessively large.

---

Zusammenfassung Schachtsicherheitspfeiler, die den Schacht vor Abbaueinwirkungen schützen sollen, werden gewöhnlich aufgrund von Erfahrungswerten bemessen.Die durch den Abbau in einem Flöz flacher Lagerung verursachten Einwirkungen auf einen saigeren Schacht sind hier nach dem Flächenelement-Prinzip ermittelt, wie Salamon es einführte. Entlang der Schachtsäule wurden die Schiefstellung, Verschiebung, horizontale und vertikale Dehnung, Krümmung und vertikale Spannung berechnet. Dabei wird der Einfluß der Querdehnungszahl, der Flöztiefe, des Pfeilerradius, der Form des Abbaufeldes und der Konvergenz im Flöz betrachtet. Diese Ergebnisse werden mit empirischen Regeln verglichen. Dabei ergab sich, daß die Tiefe des Flözes erhebliche Bedeutung hat und daß zum Schutze des Schachtes kein Pfeiler benötigt wird, wenn das abgebaute Flöz unterhalb einer bestimmten Teufe liegt. Auf der anderen Seite ist es für alle Tiefen möglich, den Schutz des Schachtes durch den Sicherheitspfeiler ersetzende geeignete Abbaumethoden zu gewährleisten.Manche Veröffentlichungen lassen erkennen, daß Schachtsicherheitspfeiler oft unnötig groß bemessen sind.

---

Résumé En général la protection des puits est accomplie par l'abandon d'une partie du gisement, le stot de puits. Les dimensions des stots sont déterminées par des méthodes empiriques.Dans cette étude c'est la méthode proposée par Salamon qui est employée; il s'agit du calcul de l'influence de l'extraction d'un élément de taille sur les morts terrains supérieurs. Cette méthode permet de calculer les déformations, la pente, la distorsion, la courbure et les tensions le long du puits. L'influence de la profondeur de la couche, de la convergence, de l'aire exploitée, du diamètre du stot de protection et des caractéristiques mécaniques du terrain ont été considérées.Les résultats indiquent l'importance particulière de la profondeur du gisement. En effet, au-delà d'une certaine profondeur un stot de protection devient superflu. D'autre part l'influence de l'aire exploitée et de la convergence dans cette région sont telles qu'il est toujours possible de remplacer l'action protectrice du stot par une protection equivalente fournie par l'emploi d'un schèma d'exploitation bien choisi.Le nombre de cas où une exploitation partielle ou entière du stot de puits a eu lieu et où son influence sur la colonne du puits a été décrite est suffisant pour permettre d'affirmer qu'en général les dimensions du stot de puits sont trop importantes.

---

---

With 11 Figures     

Biophysical impacts of climate change on some terrestrial ecosystems in Estonia

Climate warming due to the enhanced greenhouse effect is expected to have a significant impact on the natural environment and human activity in high latitudes. Because of its geography, wide coastal areas, water resources, forests, and wetlands, the environment of Estonia is sensitive to climate change and sea level rise. Climate change scenarios for Estonia were generated using a Model for the Assessment of Greenhouse-gas Induced Climate Change (MAGICC) and a regional climate change database, Scenario Generator (SCENGEN). Three alternative emission scenarios were combined with data from 14 general circulation model experiments. The assessment results of forest resources using RipFor, a forest-soil-atmosphere model, show that climate warming would enhance forest growth in Estonia resulting in increased productivity (2–9%) of harvestable timber on highly productive sites. Nutrient mobility increases greatly and in highly permeable soils with stable vegetation, increased mobility may result in nutrient losses through leaching. The assessment results of water resources using the simple water balance model, WatBal, show that the runoff regime of Estonian rivers would equilibrate and the groundwater table would rise. Climate warming would not cause any particular problems with water supply but the groundwater quality may suffer from increased leaching. Due to milder winters and increased storminess, the destruction of coastal areas, inundation of wetlands and disappearance of rare plant communities in coastal areas would be the most damaging results of climate change. Most sandy beaches high in recreational value would disappear. However, isostatic uplift and settlements inland from the present coastline reduce the risk of socio-economic decline. This revised version was published online in July 2006 with corrections to the Cover Date.     

Time Effects in Rock Mechanics by N. D. Cristescu and U. Hunsche,Wiley Series in Materials,Modelling and Computation,John Wiley & Sons,Chichester, New York,Weinheim, Brisbane,Singapore, Toronto, 1998, viii + 342 p., $115 (U.S.), ISBN 0-471-95517-5

Mathematical Geosciences -     

Distant ejecta from the Lockne marine‐target impact crater,Sweden

Abstract— The Lockne impact event took place in a Middle Ordovician (455 Ma) epicontinental sea. The impact resulted in an at least 13.5 km wide, concentric crater in the sea floor. Lockne is one of very few locations where parts of an ejecta layer have been preserved outside the crater structure. The ejecta from the Lockne impact rests on progressively higher stratigraphic levels with increasing distance from the crater, hence forming a slightly inclined discontinuity surface in the pre‐impact strata. We report on a ～30 cm thick sandy layer at Hallen, 45 km south of the crater centre. This layer has a fining upward sequence in its lower part, followed by low‐angle cross‐laminations indicating two opposite current directions. It is rich in quartz grains with planar deformation features and contains numerous, up to 15 cm large, granite clasts from the crystalline basement at the Lockne impact site. The layer is within a sequence dated to the Baltoniodus gerdae conodont subzone. The dating is corroborated by chitinozoans indicating the latest Kukruse time below and the late Idavere above the impact layer. According to the chitinozoans biostratigraphy, some erosion may have occurred because of deposition of the impact layer. The Hallen outcrop, today 45 km from the centre of the Lockne crater, is at present the most distant accessible occurrence of ejecta from the Lockne impact. It is also the most distant location so far found where the resurge of water towards the crater has affected the bottom sediments. A greater crater diameter than hitherto assumed, thus representing greater impact energy, might explain the extent of the ejecta blanket. Fluidisation of ejecta, to be expected at a marine‐target impact, might furthermore have facilitated the wide distribution of ejecta.     

Changes in the activity and tracks of Arctic cyclones

Changes in the frequency and air pressure of cyclones that enter or are formed within the Arctic basin are herein examined by applying the database of cyclones created using NCEP/NCAR re-analysis. The Arctic basin is defined as the area north of latitude 68° N. Deep cyclones with a mean sea level pressure (SLP) of below 1,000 hPa, were analysed separately from shallow cyclones. Changes in the variables in the first, last, deepest and northernmost points of cyclones were studied. The cyclones were grouped into sectors by using the point on latitude 68° N at which the cyclone entered the Arctic region. The analysis described herein shows that the frequency of incoming cyclones, i.e. those that entered the Arctic basin, increased significantly during the period 1948?C2002, but that the frequency of Arctic cyclones formed within the Arctic basin did not. The frequency of deep cyclones that entered the Arctic basin, as well as the frequency of cyclones that formed within it, clearly increased, while the frequency of shallow Arctic cyclones decreased. The most significant changes in the seasonal parameters associated with the cyclones occurred in winter. The mean annual SLP of deep cyclones decreased significantly, particularly for deep Arctic cyclones. The frequency of incoming cyclones showed an increase in the Bering Strait, Alaskan, Baffin Sea, and East Siberian sectors.     

Climatic changes in Estonia during the second half of the 20th century in relationship with changes in large-scale atmospheric circulation

Summary Trends in the time series of air temperature, precipitation, snow cover duration and onset of climatic seasons at ten stations in Estonia during 1951–2000 are analysed. Using the conditional Mann-Kendall test, these trends are compared with trends in the characteristics of large-scale atmospheric circulation: the NAO and AO indices, frequency of circulation forms according to the Vangengeim-Girs’ classification, and the northern hemisphere teleconnection indices. The objective of the study is to estimate the influence of trends in circulation on climate changes in Estonia. Statistically significant increasing trends in air temperature are detected in January, February, March, April and May, in winter (DJF), spring (MAM) and in the cold period (NDJFM). The trends in precipitation, as a rule, differ from station to station. Increasing trends are present during the cold half-year – from October until March – and also in June. Snow cover duration has decreased in Estonia by 17–20 days inland and by 21–36 days on the coast. The onsets of early spring and spring have shifted to an earlier date. Some important changes have occurred in the parameters of atmospheric circulation during 1951–2000. Intensity of zonal circulation, i.e. westerlies, has increased during the cold period, especially in February and March. Results of the conditional Mann-Kendall test indicate that the intensification of westerlies in winter is significantly related to climate changes in winter and also in spring. A negative trend in the East Atlantic Jet (EJ) index, i.e. the weakening of the westerlies in May has caused warming during that month. Decrease in northerly circulation, i.e. in frequency of circulation form C and in East Atlantic/West Russia teleconnection index (EW) is related to an increase in precipitation in October.